Reflective mask, reflective mask blank and manufacturing method therefor

ABSTRACT

A reflective mask reducing reflection of out-of-band light. The reflective mask includes a light shielding frame formed in a mask region corresponding to a boundary region of a chip on a semiconductor substrate multiply exposed. The substrate of the light shielding frame includes a layer having a different refractive index or includes pores to change the path of incident out-of-band light to thereby suppress the out-of-band light from being reflected off the conductive film. The substrate also includes a layer having a different refractive index relative to out-of-band light reflected off the conductive layer. With the reflective mask of this configuration, influence on the wiring pattern dimension can be reduced and productivity of the semiconductors can be improved.

TECHNICAL FIELD

The present disclosure relates to a reflective mask and a reflectivemask blank, and more particularly to a reflective mask, a reflectivemask blank, and a manufacturing method therefor for use in asemiconductor fabrication apparatus, for example, that uses EUV (extremeultraviolet) lithography in which an EUV source is used as a lightsource.

BACKGROUND

(EUV Lithography)

There is a trend in recent years to provide finer structures onsemiconductor devices. With this trend, there has been proposed EUVlithography in which EUV having a wavelength of approximately 13.5 nm isused as a light source. EUV lithography, in which the light-sourcewavelength is short and light absorbency is very high, has to beconducted in a vacuum. In the wavelength range of EUV, most substanceshave a refractive index slightly smaller than 1. Therefore, EUVlithography cannot use transmission-type refractive optical systems thathave been conventionally used, but has to use reflective opticalsystems. Therefore, in EUV lithography, conventional transmission-typemasks cannot be used as a photomask (hereinafter referred to as the“mask”) that is an original plate, but reflective-type masks have to beused.

(Structures of EUV Mask and Blank)

A reflective mask blank, which is an original mask of such areflective-type mask, includes a multi-layer reflective layer and anabsorbing layer formed in this order on a low thermal expansionsubstrate. The multi-layer reflective layer has a high reflectancerelative to the wavelength of an exposure light source. The absorbinglayer absorbs the wavelength of the exposure light source. The substratehas a rear face on which a rear-face conductive film is formed for anelectrostatic chuck in an exposure device. There is also an EUV maskhaving a structure in which a buffer layer is provided between amulti-layer reflective layer and an absorbing layer. In processing areflective mask blank into a reflective mask, the absorbing layer ispartially removed by electron beam (EB) lithography and etching. In thecase of the structure having a buffer layer, the absorbing layer issimilarly removed to form a circuit pattern composed of absorbingportions and reflecting portions. An optical image reflected by thereflective mask thus prepared is transferred onto a semiconductorsubstrate by way of a reflective optical system.

(Thickness of Absorbing Layer of EUV Mask and Reflectance)

In exposure methods using a reflective optical system, light is appliedto a mask surface at an incident angle which is inclined by apredetermined angle (usually 6°) relative to a vertical direction.Accordingly, in the case where the thickness of the absorbing layer islarge, the incident light casts a shadow of the pattern on thesemiconductor substrate. Since the shadowed portions will havereflection intensity smaller than in the unshadowed portions, contrastis lowered in the transferred pattern, causing blurred edges ordisplacement from designed dimensions. This is called shadowing, whichis one of the problems inherent to reflective masks.

In order to prevent blur in the pattern edges or displacement fromdesigned dimensions, an effective way is to reduce the thickness of theabsorbing layer and the height of the pattern. However, a reducedthickness of the absorbing layer degrades the light shielding propertiesof the absorbing layer, and also degrades transfer contrast and accuracyin the transferred pattern. In other words, when the absorbing layer istoo thin, the contrast necessary to keep the accuracy in the transferredpattern will no longer be obtained. In other words, an absorbing layer,which is excessively thick or thin, can cause problems. Therefore, thethickness of the absorbing layer recently is in a range of about 50 to90 nm, with the reflectance of extreme ultraviolet rays (EUV rays) ofthe absorbing layer being in a range of about 0.5 to 2%.

(Multiple Exposure of Adjacent Chips)

On the other hand, in transferring a circuit pattern onto asemiconductor substrate using a reflective mask, a plurality of chips ofthe circuit pattern are formed on a single semiconductor substrate.Between adjacent chips, there may be a region where the outer peripheralportions of the chips overlap with each other. This is caused byhigh-density arrangement of the chips, which is based on an idea ofproducing as many chips as possible per wafer to improve productivity.In this case, the overlapped region will be exposed for a plurality oftimes, four times at maximum (multiple exposure). The outer peripheralportion of each chip of the transferred pattern is also an outerperipheral portion on the mask, which is usually included in theabsorbing layer. However, as described above, since the reflectance ofEUV light of the absorbing layer is in a range of about 0.5 to 2%, theouter peripheral portion of each chip is problematically multiplyexposed. Therefore, it is necessity to provide a region in the outerperipheral portion of each chip on the mask where the effect ofshielding EUV light is higher than in a commonly used absorbing layer(hereinafter the region is referred to as a light shielding frame).

In order to improve or even solve such problems, there is proposed areflective mask in which a groove is formed through the absorbing layerand the multi-layer reflective layer of a reflective mask to therebylower the reflectance of the multi-layer reflective layer and to providea light shielding frame having high light shielding properties againstthe wavelength of an exposure light source (e.g. see JP-A-2009-212220).

However, the EUV light source, which has a peak of its radiationspectrum at a wavelength of 13.5 nm, is known to also radiate lightranging from vacuum ultraviolet outside a waveband of 13.5 nm, which iscalled out-of-band light, to the near infrared-range light at awavelength of 140 to 400 nm. In the light shielding frame proposed inJP-A-2009-212220, the out-of-band light is transmitted, as shown in FIG.12, through the substrate, and reflected off a rear-face conductive filmmade such as of chromium nitride (CrN) and formed on the EUV mask on aside opposite to a pattern side. Then, the out-of-band light is againtransmitted through the substrate for radiation toward a semiconductorsubstrate to problematically expose the resist coated on thesemiconductor substrate.

SUMMARY OF THE INVENTION

The present disclosure has been made in light of the problems set forthabove and has as its object to provide a reflective mask that reducesreflection of out-of-band light in a mask region corresponding to eachchip's boundary region multiply exposed in a semiconductor substrate.

The present disclosure has been made in light of the above problems. Afirst aspect of the present disclosure is a reflective mask blankincluding: a substrate; a multi-layer reflective layer formed on asurface of the substrate; a protective layer formed on the multi-layerreflective layer; and an absorbing layer formed on the protective layer.In the reflective mask blank, the absorbing layer includes a circuitpattern region with an outer side thereof at least partially including alight shielding frame where the absorbing layer, the protective layer,and the multi-layer reflective layer have been removed and reflectanceof EUV light and out-of-band light is low. In the reflective mask blank,the substrate of the light shielding frame includes a region whererefractive index has been changed.

A second aspect of the present disclosure is the reflective mask blankaccording to the first aspect, in which the region where refractiveindex has been changed includes a region where pores are formed tochange the refractive index.

A third aspect of the present disclosure is the reflective mask blankaccording to the first aspect, in which the region where refractiveindex has been changed includes a region where density is increased tochange the refractive index.

A fourth aspect of the present disclosure is the reflective mask blankaccording to the first aspect, in which the region where refractiveindex has been changed includes a region where the refractive index hasa gradient.

A fifth aspect of the present disclosure is a method for manufacturing areflective mask blank including steps of: irradiating a laser to asubstrate; and forming inside a substrate or near a surface of thesubstrate at least any of a region where pores are formed, a regionwhere the refractive index has been changed by increasing density, or aregion where the refractive index has a gradient.

A sixth aspect of the present disclosure is the method for manufacturinga reflective mask blank according to the fifth aspect, in which thelaser to be irradiated is any of a femtosecond laser, an attosecondlaser, a zeptosecond laser, or a yoctosecond laser.

A seventh aspect of the present disclosure is a reflective mask obtainedby patterning the absorbing layer of the reflective mask blank accordingto any of the first to fourth aspects.

The reflective mask includes a light shielding frame formed in a maskregion corresponding to a boundary region of a chip on a semiconductorsubstrate multiply exposed. The substrate of the light shielding frameincludes a region where the refractive index has been changed byincreasing density, or a region where pores have been formed, or aregion where the refractive index has a gradient. With thisconfiguration, the light path of the incident out-of-band light and thelight path of the out-of-band light reflected off the conductive filmcan be changed. Thus, there is provided a reflective mask which is ableto reduce the out-of-band light reflected off the conductive film.

With the use of the reflective mask of this configuration, influence onthe wiring pattern dimension of the semiconductor or the like can befurther reduced. Thus, the productivity of the semiconductor or the likecan be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are schematic cross sectional views each illustrating astructure of a reflective mask according to the present disclosure;

FIG. 1C is a schematic plan view illustrating the structure of thereflective mask illustrated in FIG. 1A or 1B;

FIG. 2 is a schematic side view illustrating a mask reducing out-of-bandlight by refraction in a region where the refractive index has beenchanged, according to the present disclosure;

FIG. 3 is a schematic side view illustrating a mask reducing out-of-bandlight by scattering of light in a region where the refractive index hasbeen changed, according to the present disclosure;

FIG. 4 is a set of diagrams one being a schematic side view illustratinga mask reducing out-of-band light by a region where the refractive indexhas a gradient, and the other being a diagram of the refractive indexdistribution of the region where the refractive index has a gradient,according the present disclosure;

FIGS. 5A to 5C are schematic cross sectional views each illustrating apart of a process of fabricating a reflective mask (up to formation of apattern), according to an example of the present disclosure;

FIGS. 6A and 6B are schematic cross sectional views each illustratingthe rest of the process of fabricating the reflective mask (up toformation of the pattern);

FIG. 7 is a schematic plan view illustrating a reflective mask accordingto an example of the present disclosure (up to formation of a pattern);

FIGS. 8A to 8C are schematic cross sectional views each illustrating apart of a process of fabricating a reflective mask (formation of a lightshielding frame), according to an example of the present disclosure;

FIGS. 9A to 9C are schematic cross sectional views each illustrating therest of the process of fabricating the reflective mask (formation of thelight shielding frame);

FIG. 10 is a schematic plan view illustrating a reflective maskaccording to an example of the present disclosure;

FIG. 11A is a graph illustrating reflectance of out-of-band light of areflective mask according to an example of the present disclosure;

FIG. 11B is a graph illustrating reflectance of out-of-band light of amask based on conventional art; and

FIG. 12 is a schematic diagram illustrating reflection of out-of-bandlight in a mask based on conventional art.

DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

(Configurations of Reflective Mask and Reflective Mask Blank of thePresent Disclosure)

With reference to the accompanying drawings, hereinafter will bedescribed some embodiments of the present disclosure.

First, a configuration of a reflective mask of the present disclosurewill be described. FIGS. 1A and 1B are schematic cross sectional viewsillustrating structures of reflective masks 101 and 102, respectively,of the present disclosure. FIG. 1C is a schematic plan view illustratingthe reflective mask 101 or 102 illustrated in FIG. 1A or 1B as viewedfrom above.

In each reflective mask according to the present embodiment, a circuitpattern is formed on an absorbing layer. In the present embodiment, areflective mask blank is defined to be a flat mask before formation of acircuit pattern in an absorbing layer. In the following description,when a reflective mask blank is referred to, it means a mask with a flatabsorbing layer before a circuit pattern is formed.

The reflective masks, or reflective mask blanks, 101 and 102 illustratedin FIGS. 1A and 1B each include a multi-layer reflective layer 2, aprotective layer 3, and an absorbing layer 4 formed in this order on asurface of a substrate 1. The substrate 1 has a rear face on which aconductive film 5 is formed. A buffer layer may be provided between theprotective layer 3 and the absorbing layer 4. The buffer layer isprovided to prevent the protective layer 3, as an underlayer, from beingdamaged when the mask pattern of the absorbing layer 4 is corrected.

The reflective masks, or reflective mask blanks, 101 and 102 of thepresent disclosure each include a pattern region 10 where the absorbinglayer 4 will be processed (in the case of a reflective mask blank) orhas been processed (in the case of a reflective mask), a light shieldingframe 11 formed in an outer peripheral portion of the pattern region 10,and a region 12 inside the substrate 1. The light shielding frame 11 isformed by removing the absorbing layer 4, the protective layer 3, andthe multi-layer reflective layer 2, as well as the buffer layer, ifprovided. In the region 12, the refractive index has been changed bylaser irradiation.

FIG. 2 is a schematic side view illustrating a mask reducing out-of-bandlight by refraction in the region where the refractive index has beenchanged, according to the present disclosure. A laser is irradiated tothe inside of the substrate 1 to form a region 20 where the refractiveindex is small to thereby reduce out-of-band light. The mechanism forreducing out-of-band light is that, when out-of-band light 301 isincident on the region 20 having a small refractive index, the directionof the light is changed by refraction, and the out-of-band light isprevented from being transferred toward the semiconductor substrate ifthe out-of-band light is reflected off the rear-face conductive film.The region having a small refractive index can be provided by formingpores, for example. The refractive index of the substrate is about 1.5and the refractive index of the pores is about 1. Taking account ofthis, in order to prevent the out-of-band light from being transferredtoward the semiconductor substrate if the out-of-band light is reflectedoff the rear-face conductive film, the region 20 has to be formed beinginclined. Since the out-of-band light 301 is incident at an angle of 6°,the region 20 is required to have an inclination of least θ=25° orgreater. Further, the region 20 is required to be aligned with the lightshielding frame and have a width equal to that of the light shieldingframe. Forming the region 20 in this way, the direction of light ischanged by refraction. As a result, the out-of-band light reflected offthe rear-face conductive film can be prevented from passing through thelight shielding frame 11 and being transferred to the semiconductorsubstrate.

FIG. 3 is a schematic side view illustrating a mask reducing out-of-bandlight using scattering of light in a region where the refractive indexhas been changed, according to the present disclosure. Forming a region21 where the refractive index has been changed by irradiating with alaser, out-of-band light can be reduced. The mechanism is that theout-of-band light 301, when being incident on the region 21, isscattered due to the changed refractive index to thereby reduce theout-of-band light reflected off the rear-face conductive film. Theregion 21 having a changed refractive index can be formed by formingpores in the substrate or increasing density of the substrate. Theregion 21 is aligned with the light shielding frame and is permitted tohave a width equal to that of the light shielding frame. Taking accountof the ease of laser irradiation from the rear face, the region 21 ispreferably arranged near the center of the substrate in a thicknessdirection, i.e. at a distance d (=3 mm) from the rear face as shown inFIG. 3. Forming the region 21 to scatter light in this way, theout-of-band light reflected off the rear-face conductive film can bereduced. If a part of the scattered out-of-band light is verticallyincident and reflected off the rear face conductive film, the light isscattered by the region 21. As a result, the out-of-band light passingthrough the light shielding frame 11 can be reduced to almost zero.

FIG. 4 is a schematic side view illustrating a mask reducing theout-of-band light by a region having a refractive index gradient,according to the present disclosure. A laser is irradiated into thesubstrate to form a region 22 having a refractive index gradient asshown in a graph of FIG. 4 to thereby reduce the out-of-band light. Themechanism is that the incident out-of-band light 301, when transmittingthrough the region having a refractive index gradient, is deflected to ahigher refractive index portion, and the out-of-band light is nottransferred toward the semiconductor substrate if the out-of-band lightis reflected off the rear-face conductive film. The region having arefractive index gradient can be formed by changing the density of thesubstrate by laser irradiation. When the difference in gradient of therefractive index is about 0.02 (refractive index difference/mm) orgreater, the out-of-band light incident on the center of the lightshielding frame 11 can be deflected to a region having no influence onthe transfer toward the semiconductor substrate. The region 22 isrequired to be aligned with the light shielding frame, while beingextended from the front face to rear face, or throughout the depth, ofthe substrate 1, and to have a width equal to that of the lightshielding frame. Forming the region 22 in such a way of deflectinglight, the out-of-band light reflected off the rear-face conductive filmcan be reduced.

(Configuration of Reflective Mask of the Present Disclosure: Multi-layerreflective layer, Protective Layer, and Buffer Layer)

The multi-layer reflective layer 2 of FIG. 1A is designed to achieve areflectance of about 60% for EUV light. The multi-layer reflective layer2 is a laminated film in which 40 to 50 pairs of Mo layers and Si layersare alternately laminated. The protective layer 3, which is the topmostlayer, is formed of a ruthenium (Ru) layer with a thickness of 2 to 3 nmor a silicon (Si) layer with a thickness of about 10 nm. The layeradjacently located below the Ru layer is a Si layer. Since Mo and Siabsorb less EUV light (have low extinction coefficient) and have a largerefractive index difference for EUV light, reflectance can be increasedin the interface between the Si layer and the Mo layer. This is thereason why Si and Mo are used for the multi-layer reflective layer 2.The protective layer 3, when made of Ru, can serve as a stopper inprocessing the absorbing layer 4 or as a protective layer against achemical solution in cleaning the mask. When the protective layer 3 ismade of Si, a buffer layer may be arranged between the protective layer3 and the absorbing layer 4. The buffer layer is provided to protect theSi layer in etching the absorbing layer 4 or in correcting the pattern.The Si layer is the topmost layer of the multi-layer reflective layer 2and provided adjacently below the buffer layer. The buffer layer is madeof chromium (Cr) or a nitrogen compound thereof (CrN).

(Configuration of Reflective Mask of the Present Disclosure: AbsorbingLayer)

The absorbing layer 4 shown in FIG. 1A is made of a nitrogen compound(TaN) of tantalum (Ta) having a high EUV absorptivity. As othermaterials, the absorbing layer 4 may be made of tantalum boron nitride(TaBN), tantalum silicon (TaSi), tantalum (Ta), or oxides of thesematerials (TaBON, TaSiO, and TaO). The absorbing layer 4 shown in FIG.1A may have a two-layer structure including an upper layer as a lowreflective layer which is antireflective to UV light having a wavelengthof 190 to 260 nm. The low reflective layer is provided to enhancecontrast to the inspection wavelength of a mask defect inspection deviceand to improve inspectability.

(Configuration of Reflective Mask of the Present Disclosure: Rear-FaceConductive Film)

The conductive film 5 shown in FIG. 1A is made of CrN in general. Sincethe conductive film 5 only has to be electrically conductive, anymaterial containing a metallic material can be used. Although FIG. 1Ashows a configuration including the conductive film 5, the mask blank,or the mask, may be configured without including the conductive film 5.

(Method for Manufacturing Reflective Mask of the Present Disclosure)

A method for forming the light shielding frame of the reflective mask ofthe present disclosure will be described in detail. First, a reflectivemask 211 shown in FIG. 8A is subjected to photolithography orelectron-beam lithography to form a resist pattern with only a lightshielding frame portion being opened. Subsequently, the absorbing layer4 and the protective layer 3 in the opening of the resist pattern areremoved by dry etching using a fluorine-based gas or chlorine-based gas,or both. Subsequently, the multi-layer reflective layer 2 in the openingis penetrated and removed by dry etching using a fluorine-based gas orchlorine-based gas, or both, or by wet etching using an alkalinesolution or an acid solution.

The reason why a fluorine-based gas or chlorine-based gas, or both areused in penetrating and removing the multi-layer reflective layer 2 bydry etching is that these gases have etchability to Mo and Si which arethe materials of the multi-layer reflective layer. Fluorine-based gasesthat can be used for etching include CF₄, C₂F₆, C₄F₈, C₅F₈, CHF₃, SF₆,ClF₃, Cl₂, and HCl.

In penetrating and removing the multi-layer reflective layer 2 by wetetching, the etchant to be used is required to be suitable for etchingMo and Si which are the materials of the multi-layer reflective layer 2.For example, as an alkaline solution, a solution of tetramethyl ammoniumhydroxide, (TMAH), potassium hydroxide (KOH), or ethylene diaminepyrocatechol (EDP) is appropriately used. As an acid solution, a liquidmixture of nitric acid and phosphoric acid is appropriately used.Hydrogen fluoride, sulfuric acid, or acetic acid may be added to theliquid mixture.

As described above, a reflective mask that reduces the reflection ofout-of-band light can be obtained as an EUV mask having a lightshielding region from which the multi-layer reflective layer has beenremoved.

Examples

The following description sets forth an example of a method formanufacturing the reflective mask according to the present disclosure. Areflective mask blank 201 shown in FIG. 5A was used in the presentexample. The mask blank 201 includes a substrate 1, a multi-layerreflective layer 2, a protective layer 3 and an absorbing layer 4, whichare laminated in this order from bottom to top. The multi-layerreflective layer 2 includes 40 pairs of Mo layers and Si layers designedto have a reflectance of about 64% relative to EUV light having awavelength of 13.5 nm. The protective layer 3 is made of Ru and has athickness of 2.5 nm. The absorbing layer 4 is made of TaSi and has athickness of 70 nm.

In the mask blank, before forming the rear-face conductive film 5, alaser is irradiated to the substrate 1 to form pores to thereby providea region 12 where the refractive index has been changed. The region 12is at a position spaced apart by 3 μm from a 10 cm×10 cm main patternregion at the center of the mask where the light shielding frame of themask of the present disclosure is to be formed. In addition, the region12 is located so as to be aligned with the region serving as the lightshielding frame and has a width of 5 mm equal to that of an opening ofthe region serving as the light shielding frame.

The pores were formed using a femtosecond laser device under theconditions of 800 nm wavelength, 120 fs pulse width, and 200 kHzfrequency.

Then, a chemically amplified positive resist 9 (FEP171 manufactured byFUJIFILM Electronic Materials Co., Ltd.) was coated onto the mask blankso as to have a thickness of 300 nm (FIG. 5B), followed by producing apattern using an electron beam lithography exposure system (JBX9000manufactured by JEOL Ltd.). The resultant mask blank was subjected topost exposure baking (PEB) at a temperature of 110° C. for 10 minutesand spray development (SFG3000 manufactured by Sigmameltec LTD.),thereby forming a resist pattern on the resist (FIG. 5C).

Subsequently, the absorbing layer 4 was etched with CF₄ plasma and Cl₂plasma using a dry etching device (FIG. 6A), followed by separating theresist and cleaning. In this way, a reflective mask 211 having anevaluation pattern (pattern region 10) as shown in FIG. 6B was prepared.The evaluation pattern was made of lines and spaces provided at a ratioof 1:1 with a dimension of 200 nm, and arranged at the center of themask. The size of the pattern region 10 was 10 cm×10 cm. FIG. 7 shows aschematic plan view of the reflective mask 211 with the pattern region10.

Subsequently, a light shielding frame was formed on the pattern region10 of the reflective mask 211, the pattern region 10 being provided withthe above evaluation pattern. Specifically, an i-line resist 29 wascoated onto the reflective mask 211 (FIG. 8A) so as to have a thicknessof 500 nm (FIG. 8B). Then, a pattern was drawn on the i-line resist 29using an i-line lithography exposure system (ALTA), followed bydevelopment. Thus, a resist pattern was formed, in which the regionserving as the light shielding frame later was open (FIG. 8C). Theopening of the resist pattern had a width of 5 mm, and was located beingspaced apart by 3 from the 10 cm×10 cm main pattern region at the maskcenter.

Subsequently, the absorbing layer 4 and the multi-layer reflective layer2 in the opening of the resist were penetrated and removed by verticaldry etching with CHF₃ plasma using a dry etching device (FIGS. 9A and9B). The dry etching was conducted under the conditions where thepressure in the dry etching device was 50 mTorr, inductively coupledplasma (ICP) power was 500 W, reactive ion etching (ME) power was 2000W, a CHF₃ flow rate was 20 sccm, and treatment time was 6 minutes. As aresult, a shape as shown in FIG. 9B was obtained.

Finally, using a sulfuric acid-based remover and an ammonia hydrogenperoxide solution, the resist was separated, followed by cleaning, whichwas further followed by dry etching to remove the remaining resist (FIG.9C). FIG. 10 shows a reflective mask 221 prepared in the presentexample.

Subsequently, reflectances of both the reflective mask according to thepresent disclosure and a conventional reflective mask with a lightshielding frame were measured in the light shielding frame regions. As aresult, it was confirmed that the reflectance of the reflective maskwith the light shielding frame of the present disclosure could reducereflectance, as shown in FIG. 11A, by about 40% at a wavelength in arange of 200 nm to 400 nm compared to the reflectance of theconventional reflective mask with the light shielding frame, as shown inFIG. 11B.

As described above, a reflective mask that reduced the reflection ofout-of-band light could be prepared.

For example, the present disclosure is useful for reflective masks.

What is claimed is:
 1. A reflective mask blank comprising: a substrate;a multi-layer reflective layer formed on a surface of the substrate; aprotective layer formed on the multi-layer reflective layer; and anabsorbing layer formed on the protective layer, wherein the absorbinglayer includes a circuit pattern region with an outer side thereof atleast partially including a light shielding frame where the absorbinglayer, the protective layer, and the multi-layer reflective layer havebeen removed and reflectance of EUV light and out-of-band light is low;and wherein the substrate of the light shielding frame includes a regionwhere a refractive index has been changed, the region being inside thesubstrate.
 2. The reflective mask blank of claim 1, wherein the regionwhere the refractive index has been changed includes a region wherepores are formed to change the refractive index.
 3. A reflective maskobtained by patterning the absorbing layer of the reflective mask blankof claim
 2. 4. The reflective mask blank of claim 1, wherein the regionwhere the refractive index has been changed includes a region wheredensity is increased to change the refractive index.
 5. A reflectivemask obtained by patterning the absorbing layer of the reflective maskblank of claim
 4. 6. The reflective mask blank of claim 1, wherein theregion where the refractive index has been changed includes a regionwhere the refractive index has a gradient.
 7. A reflective mask obtainedby patterning the absorbing layer of the reflective mask blank of claim6.
 8. A reflective mask obtained by patterning the absorbing layer ofthe reflective mask blank of claim
 1. 9. A method for manufacturing areflective mask blank comprising steps of: irradiating a substrate usinga laser substrate; and forming, inside the substrate, at least a regionwhere a refractive index has been changed by increasing density.
 10. Themethod for manufacturing a reflective mask blank of claim 9, wherein thelaser is a laser selected from the group consisting of a femtosecondlaser, an attosecond laser, a zeptosecond laser, or a yoctosecond laser.